using System.Collections.Concurrent;
using CMSMicroservice.Application.Common.Exceptions;
using CMSMicroservice.Application.Common.Interfaces;
using Microsoft.Extensions.Logging;

namespace CMSMicroservice.Infrastructure.Services;

/// <summary>
/// In-process keyed semaphore lock for payment operations.
/// Safe for multi-threaded gRPC/MediatR handlers within a single CMS instance.
/// </summary>
public sealed class UserPaymentLockService : IUserPaymentLock, IDisposable
{
    private static readonly TimeSpan VerifyWaitTimeout = TimeSpan.FromSeconds(30);
    private static readonly TimeSpan StaleEntryAge = TimeSpan.FromMinutes(30);
    private static readonly TimeSpan CleanupInterval = TimeSpan.FromMinutes(5);

    private readonly ConcurrentDictionary<string, LockEntry> _entries = new();
    private readonly ILogger<UserPaymentLockService> _logger;
    private readonly Timer _cleanupTimer;
    private int _disposed;

    public UserPaymentLockService(ILogger<UserPaymentLockService> logger)
    {
        _logger = logger;
        _cleanupTimer = new Timer(_ => CleanupStaleEntries(), null, CleanupInterval, CleanupInterval);
    }

    public Task<T> ExecuteAsync<T>(
        string scope,
        PaymentLockStrategy strategy,
        Func<CancellationToken, Task<T>> action,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(scope);
        ArgumentNullException.ThrowIfNull(action);

        return ExecuteCoreAsync(scope, strategy, action, cancellationToken);
    }

    public async Task ExecuteAsync(
        string scope,
        PaymentLockStrategy strategy,
        Func<CancellationToken, Task> action,
        CancellationToken cancellationToken = default)
    {
        ArgumentException.ThrowIfNullOrWhiteSpace(scope);
        ArgumentNullException.ThrowIfNull(action);

        await ExecuteCoreAsync(
            scope,
            strategy,
            async ct =>
            {
                await action(ct);
                return true;
            },
            cancellationToken);
    }

    private async Task<T> ExecuteCoreAsync<T>(
        string scope,
        PaymentLockStrategy strategy,
        Func<CancellationToken, Task<T>> action,
        CancellationToken cancellationToken)
    {
        var entry = _entries.GetOrAdd(scope, static _ => new LockEntry());
        entry.Touch();

        var waitTimeout = strategy == PaymentLockStrategy.FailFast
            ? TimeSpan.Zero
            : VerifyWaitTimeout;

        Interlocked.Increment(ref entry.WaiterCount);

        var acquired = false;
        try
        {
            acquired = await entry.Semaphore.WaitAsync(waitTimeout, cancellationToken);
            if (!acquired)
            {
                _logger.LogWarning(
                    "Payment lock busy. Scope={Scope}, Strategy={Strategy}",
                    scope,
                    strategy);

                throw new PaymentInProgressException(
                    strategy == PaymentLockStrategy.FailFast
                        ? "درخواست پرداخت دیگری در حال پردازش است. لطفاً صبر کنید."
                        : "تأیید پرداخت در حال انجام است. لطفاً چند لحظه صبر کنید.");
            }

            entry.Touch();
            return await action(cancellationToken);
        }
        finally
        {
            if (acquired)
                entry.Semaphore.Release();

            if (Interlocked.Decrement(ref entry.WaiterCount) == 0 && entry.CanRemove)
                _entries.TryRemove(scope, out _);
        }
    }

    private void CleanupStaleEntries()
    {
        if (Interlocked.CompareExchange(ref _disposed, 0, 0) == 1)
            return;

        var cutoff = DateTime.UtcNow - StaleEntryAge;
        foreach (var (scope, entry) in _entries)
        {
            if (entry.LastUsedUtc < cutoff && entry.CanRemove)
                _entries.TryRemove(scope, out _);
        }
    }

    public void Dispose()
    {
        if (Interlocked.Exchange(ref _disposed, 1) == 1)
            return;

        _cleanupTimer.Dispose();

        foreach (var entry in _entries.Values)
            entry.Semaphore.Dispose();

        _entries.Clear();
    }

    private sealed class LockEntry
    {
        public SemaphoreSlim Semaphore { get; } = new(1, 1);
        public int WaiterCount;
        public DateTime LastUsedUtc { get; private set; } = DateTime.UtcNow;

        public void Touch() => LastUsedUtc = DateTime.UtcNow;

        public bool CanRemove =>
            Volatile.Read(ref WaiterCount) == 0 && Semaphore.CurrentCount == 1;
    }
}